Magneto-responsive device



June 26, 1956 w. c. DUNLAF, JR 2,752,434

MAGNEITO-RESPONSIVE DEVICE Original Filed Oct. 19, 1949 Fig.1

William Cram/{ ord Dunlap J1";

His Attorneg.

United States Patent "ice MAGNETO-RESPONSIVE DEVICE William CrawfordDunlap, Jr., Schenectady, N. Y., as-

signor to General Electric Company, a corporation of New York Originalapplication October 19, 1949, Serial No. 122,243. Divided and thisapplication March 22, 1952, Serial No. 278,055

4 Claims. (Cl. 179 171) This invention relates to a magneto-responsivedevice system employing a semi-conductor, the electrical resistance ofwhich is controllable by a magnetic field. This application is adivision of my application, Serial No. 122,243, filed October 19, 1949,entitled, Magneto-Responsive Device Control System, and assigned to thepresent assignee, which is abandoned.

Known magneto-responsive systems which are capable of producing anelectrical signal output are generally of the type employing amagneto-inductive transformer havin a variably excited primary windingor a magneto-inductive generator having a physically relatively movablemagnetic armature. in any of these magneto-inductive systems the outputvoltage signal is dependent upon a rate of change in a magnetic fieldwhich is produced in the transformer by a changing current in a primarywinding, and in the generator by the relative movement between themagnetic parts. However, it is often desirable to obtain an electricalsignal which subsists when no change occurs and when no rate of changeexists, but a signal which nevertheless indicates the magnitude of adirect current excitation signal in an apparatus with relatively fixedparts or indicates the relative positions of relatively movable parts,while at the same time giving an indication of magnitude of input signalor change of relative position in terms of the magnitude of excitationor instantaneous position in these devices.

It is, therefore, an object of my invention to provide amagneto-responsive device system which is a direct current amplifier aswell as an alternating current amplifier.

it is a further object of my invention to provide a magneto-responsivedevice system which may be used as a position indicator to indicate therelative positions of two relatively movable parts in terms of theelectrical resistance of an output circuit or the magnitude of an.electrical output derived therefrom.

A still further object of my invention is to provide amagneto-responsive device having an unusually high degree of resistancevariation in response to a given small change in magnetic fieldexcitation.

The invention, therefore, generally comprises an arrangement including apaper-thin semi-conductor element the resistance of which is responsiveto a magnetic field :therethrough, an apparatus for the creation of sucha magnetic field in accordance with an input signal, and leadconnections for the measurement of the resistance of the semi-conductor.

The features which I desire to protect are pointed out withparticularity in the appended claims. The invention itself, togetherwith further objects and advantages thereof, may be best understood byreference to the following description taken in connection with thedrawing, in which Fig. 1 shows the magneto-responsive device system ofthis invention including electrical circuit components which are shownschematically; Fig. 2 is an enlarged detail view of a second embodimentof the invention wherein the semi-conductor element is in the form2,752,434 Patented June 26, 1956 of a Very thin sheet or stripmechanically supported and protected by insulating members; and Fig. 3is a corresponding view of a third embodiment of the invention whereinno relative movement between the semi-conductor element and the magneticstructure is provided for, whereby the gap in the magnetic structure forthe accomrnodat n of the semi-conductor element and insulating membersis held to a minimum dimension.

Referring more particularly to the drawing, in Fig. 1

there is shown a magneto-responsive device system which includes asemi-conductor element or member 2 held in a fixed position by clampingmembers 3. The semiconductor itself may be characterized as amagneto-responsive device. A magnetic structure 4, with pole pieces 5and 6, is positioned to set up a magnetic field through semi-conductingmember 2. Magnetic structure 4 is adapted for movement along guides 7and 8. This movement may occur in response to movements of a movablebody 9 transmitted through a suitable linkage such as that comprisinglinks 16 and 11 and lever 12. Magnetic structure 4 may be a permanentmagnet or an electromagnet with an excitation winding 13 which may beenergized from a source of signal voltage l4. Suitable electricalconnections to the semi-conductor element 2 are made at 15 and 16. Aresistance measuring circuit provided at these connections comprises asource of electrical energy such as battery 17 and a load resistor 13which are connected in series with the semi-conductor element 2. Thevoltage of battery 17 is, therefore, impressed across the EIJl-COBdUClGland the load resistor 18 in series. The relative magnitudes of therespective voltages across these two resistances may be measured by adevice such as an electron discharge device 19 having a controlelectrode 29 to which voltage across resistor 13 may be applied. Theoutput of device 19 may be fed to an indicator or control device 21 forestablishing a control in accordance with the input signal from source14.

In the operation of the magneto-responsive device of this invention, asuitable electrical signal which may comprise an alternating currentvoltage or a direct current voltage or a combination of the two may besupplied from signal voltage source 14 and used to energize winding 13to create a magnetic field in magnetic structure 4- in accordancetherewith. The magnetic field which then exists between pole pieces 5and 6 passes through semi-conductor element 2. Element 2 comprises asemiconductor material, such as germanium, whose electrical resistanceis dependent upon the flux density of a magnetic field therethrough. Inthis connection it has been found that, in an element of germanium, amagnetic field flux density of 12,000 gauss causes as much as a 25%increase in resistivity over the value of resistivity with no magneticfield. Element 2 is preferably of a highly purified type of germaniumcharacterized by freedom from such impurities as aluminum, tin, arsenic,and gallium, since the presence of these elements, even in smallamounts, lowers the resistivity of the germanium. Germanium having anunmagnetized resistivity above 5 ohm-centimeters is preferable. Suchhigh resistivity is desired because the increase of resistance ofgermanium in the presence of a magnetic field, hereinafter referred toas the magneto-resistive effect, is proportional to the unmagnetizedresistivity of the material. Semi-conductors which exhibit this effectare hereinafter referred to as semi-conductors having magneto-resistiveproperties.

Element 2 is connected in series with registor 18 and a voltage isimpressed across both by means of battery 17. Variations in theresistance of element 2 due to the magneto-resistive effect causevariations in the proportion of the supply voltage from battery 17 whichexists at a given time across element 2 and resistance 18. As a result,the voltage at the common connection between element 2 and resistor 18supplied to control electrode 20 of electron discharge device 19fluctuates with respect to ground. The signal thus derived is amplifiedby electron discharge device 19 and supplied to an indicator or controldevice 20. Device 2 may be any visual or audible indicator suitable tobring attention to the condition causing the signal from source 14.Alternatively, it may comprise an automatic control device forcontrolling temperature or any other condition or function controllableby an electrical voltage.

The magneto-responsive device system of this invention may also indicateor control in response to physical movements of a movable body such as9. Through a suitable linkage such as that provided by members 10, 11and 12 movement of body 9 causes a corresponding movement of magneticstructure 4 so that pole pieces 5 and 6 gradually assume a new position,for instance as at 5a and 6a. In this new position, the magnetic fieldprovided by a magnetic field structure 4 no longer traverses thesemi-conductor element 2 and the resulting change in the resistivity ofelement 2 effects an indication or control signal at indicator orcontrol device 21 in accordance with the new position of movable body 9.

Element 2 may comprise a slab or water of semi-conductor material andthe electrical connections at 15 and 16 may be made by solderingsuitable conductors to the semi-conductor element at the edges thereof.Pure tin solder is preferably used, although other soldering materialsrnay be found to be satisfactory.

Fig. 2 is a detail view of an embodiment of the invention wherein thesemi-conductor element 2 comprises a sheet or strip of the order of afew, preferably less than five, thousandths of an inch in thickness,which may be characterized as paper thin. The resistance of the elementis thus increased to increase the magneto-resistive etfect, which, asstated above, is proportional to the resistance. Suitable members 22 ofrigid insulating material may be used in this embodiment to impart structural strength to element 2 since the semi-conductor material itself,because of its thinness, is structurally weak.

In Fig. 3 there is shown a structure similar to that of Fig. 2 which maybe employed where there is to be no movement of magnetic structure 4 andpole pieces 5 and 6 relative to element 2. In this arrangement, theinsulating members 22 and the semi-conductor element 2 may be tightlyfitted and supported between pole pieces 5 and 6. Also, insulatingmembers 22 may be reduced to a minimum thickness since the structuralstrength for the cantilever construction of Fig. 2 is not needed,adequate electrical insulation being the only critical requirement. Bymeans of this construction, the gap between pole pieces 5 and 6 may bekept to a minimum dimension so that a lower energy input is required formagnetic structure 4 to obtain the desired flux density insemi-conductor element.2. Clamping members 3 are unnecessary since theelement is supported by pole pieces 5 and 6.

It will be seen from the above description that this invention providesfor a magneto-responsive device system which produces a signal inresponse to, and proportional to the strength of, a magnetic field andindependent of the rate of change thereof which will provide indicatoror control voltages useful in many applications.

While only certain preferred embodiments of the invention have beenshown by way of :Jration, many modifications will occur to those skilledin the art and it is, therefore, to be understood that the appendedclaims are intended to cover all such modifications as fall within thetrue spirit and scope of the invention.

What i claim as new and desire to secure by Letters Patent of the UnitedStates is:

V 1. A magneto-responsive device system for providing an amplifiedreplica of a signal voltage comprising an electromagnetic structurehaving a winding excited in accordance with said signal voltage, apaper-thin high resistance germanium sheet arranged entirely within agap in said magnetic structure, the resistance of said germanium sheetbeing controlled by a magnetic field set up by said structure,sheet-supporting insulating members secured to opposite faces of saidsheet, connections at opposite edges of said sheet for supplying acurrent through said germanium .sheet in a direction perpendicular tosaid magnetic field to derive an output voltage between said connectionsvarying in accordance with the resistance of said sheet, a voltagesource connected to one of said connections, and a load elementconnected to the remaining connection, said voltage source, saidgermanium sheet, and said load element being connected in series circuitrelationship.

2. A magneto-responsive control device comprising a paper-thin highresistivity germanium sheet having magneto-resistive properties, anelectromagnetic structure having closely spaced magnetic poles,sheet-supporting insulating members secured to and between each pole anda respective major face of said sheet, connections to opposite edges ofsaid sheet for supplying a current therethrough, a voltage sourceconnected to one of said connections, and a load element connected tothe remaining connection, said voltage source, said germanium sheet, andsaid load element being connected in series circuit relationship.

3. A magneto-responsive control device comprising an electromagnethaving closely spaced pole pieces, a magneto-resistive element supportedbetween said pole pieces comprising a paper-thin high resistivitygermanium sheet having insulating supporting plates secured to oppositefaces of said sheet, connections to opposite edges of said germaniumsheet for supplying a current therethrough, a voltage source connectedto one of said connections, and a load element connected to theremaining connection, said Voltage source, said germanium sheet, andsaid load clement being connected in series circuit relationship.

4. A magneto-responsive device system comprising a magnet having spacedaligned pole pieces, a magnetoresistive element comprising a paper-thinhigh resistivity germanium sheet having insulating supporting platessecured to its opposite major faces, said element being supported withinthe magnetic field produced between said pole pieces, connections toopposite edges of said sheet for supplying a current therethrough, avoltage source connected to one of said connections, a load elementconnected to the remaining connection, said voltage source, saidgermanium sheet, and said load element being connected in series circuitrelationship, and means for producing relative movement between saidelement and said magnet to vary the intensity of the magnetic fieldthrough said element.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Non-Rectifying Germanium from the Physical Review, vol. 74,issue 8, page 976, published Aug. 15, 1948.

1. A MAGNETO-RESPONSIVE DEVICE SYSTEM FOR PROVIDING AN AMPLIFIED REPLICA OF A SIGNAL VOLTAGE COMPRISING AN ELECTROMAGNETIC STRUCTURE HAVING A WINDING EXCITED IN ACCORDANCE WITH SAID SIGNAL VOLTAGE, A PAPER-THIN HIGH RESISTANCE GERMANIUM SHEET ARRANGED ENTIRELY WITHIN A GAP IN SAID MAGNETIC STRUCTURE, THE RESISTANCE OF SAID GERMANIUM SHEET BEING CONTROLLED BY A MAGNETIC FIELD SET UP BY SAID STRUCTURE, SHEET-SUPPORTING INSULATING MEMBERS SECURED TO OPPOSITE FACES OF SAID SHEET, CONNECTIONS AT OPPOSITE EDGES OF SAID SHEET FOR SUPPLYING A CURRENT THROUGH SAID GERMANIUM SHEET IN A DIRECTION PERPENDICULAR TO SAID MAGNETIC FIELD TO DERIVE AN OUTPUT VOLTAGE BETWEEN SAID CONNECTIONS VARYING IN ACCORDANCE WITH THE RESISTANCE OF SAID SHEET, A VOLTAGE SOURCE CONNECTED TO ONE OF SAID CONNECTIONS, AND A LOAD ELEMENT CONNECTED TO THE REMAINING CONNECTION, SAID VOLTAGE SOURCE, SAID GERMANIUM SHEET, AND SAID LOAD ELEMENT BEING CONNECTED IN SERIES CIRCUIT RELATIONSHIP. 